Patent GB-568890-A (GB)
Title: Improvements in or relating to the melt extrusion of synthetic polymers
IPC: A61C15/04
Filed: 1943-03-01
Abstract: <PICT:0568890/IV/1> A normally solid ethylene polymer is subjected to a heat treatment at a temperature at least 85 DEG  C. above its melting point and in the absence of oxygen so as to improve its solubility in organic solvents and render it more suitable for use in extrusion processes for the production of artificial filaments, tapes, films, tubes and other articles.  The heat treatment may be combined with an extrusion operation by extruding the ethylene polymer at a temperature at least 85 DEG  C. above its melting point and in the absence of oxygen.  The temperature may be 185-450 DEG  C. The treatment may be carried out in a closed reaction vessel, in a stainless steel coil immersed in a bath of molten lead, or in a glass tube immersed in a vapour bath.  In an example, an ethylene polymer of molecular weight about 20,000 and of melting point 110 DEG  C. is pressure moulded to form a rod which is then forced into a melting chamber.  The molten polymer is extruded at 195-299 DEG  C. into the air to form filaments which are stretched by a collecting bobbin and subsequently further stretched while immersed in hot water.  In another example, an ethylene polymer is melted in an atmosphere of nitrogen under pressure and is then subjected to vacuum to remove gas bubbles.  It is extruded at 272 DEG  C. through a slot orifice directly into cold water to form a smooth transparent film.  In another example, an ethylene polymer, which is incompletely soluble in xylene at the boiling point, is heated with tetrahydronaphthalene in an atmosphere of nitrogen in a closed vessel for 3 hours at 285 DEG  C.  The vessel is cooled to 90 DEG  C. and the viscous solution is removed.  On cooling further, the polymer separates as a gelatinous mass.  This is filtered off and washed with petroleum ether.  The solid is dried in an atmosphere of nitrogen.  The product is completely soluble in xylene at the boiling point and it has a greater tensile strength than the untreated polymer.  In another example, an ethylene polymer, which gives very viscous solutions in boiling xylene, is formed into narrow strips and placed in a tube from which the air is evacuated and replaced by nitrogen.  The tube is immersed in a vapour bath of boiling hexachlorobenzene for one hour.  The product is readily soluble in hot xylene to form solutions which may be used for casting films.  The treated polymers may be used for making dental floss, tapered or cylindrical bristles for brushes of various kinds, surgical sutures, fishing leaders, textile yarns, screens, p  tubes, sleeves, straws and films.  Filaments or fibres may be wound around electrical conductors and shrunk thereon by application of heat.  Bristles may be set by heating them at constant length to a temperature approaching the melting point. Luminescent films may be obtained by incorporating luminescent pigments such as zinc sulphide, strontium sulphide, or calcium sulphide.  As shown in Fig. 1, ethylene polymer in rod form 4 is forced through a sealing ring 5 against the heated conical walls of the melt chamber 1 by a plunger 6.  Molten polymer passes from channel 13 through filters 14 and through spinneret 16 to form filaments 15.  Specification 552,227 is referred to.